There are at least five genetically distinct collagen types whose degradation may be controlled independently. The initial step of collagen degradation is performed by collagenase. We were the first to find that type IV basement membrane collagen and type V collagen is not degraded by human skin collagenase suggesting that a separate collagenase may degrade types IV and V collagen. A collagenase which preferentially degrades type IV collagen has been derived from metastatic tumor cells and from mammary epithelium. This collagenase has been purified 1000-fold and its cleavage products have been partially characterized. We are further studying the secretion rate of this enzyme by a wide variety of cell types both normal and malignant.